Tesla’s $1 trillion valuation made sense only if investors believed the electric car company was on a path to dominate the auto industry the way Apple rules smartphones or Amazon commands online retailing.

But Tesla’s shares have declined more than 40 percent since April 4 — a much steeper fall than the broad market, vaporizing more than $400 billion in stock market value. And the tumble has called attention to the risks that the company faces. These include increasing competition, a dearth of new products, lawsuits accusing the company of racial discrimination and significant production problems at Tesla’s factory in Shanghai, which it uses to supply Asia and Europe.

Mr. Musk has not helped the stock price by turning his bid to buy Twitter into a financial soap opera. His antics have reinforced the perception that Tesla lacks an independent board of directors that could stop him from doing things that might damage the company’s business and brand.

“From a corporate good governance perspective Tesla has a lot of red flags,” said Andrew Poreda, a senior analyst who specializes in socially responsible investing at Sage Advisory Services, an investment firm in Austin, Texas. “There are almost no checks and balances.”